Child safety seat base



FIG. 1 is a top, front, right side perspective view of a child safety seat base, showing our new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines in the drawings depict portions of the child safety seat base that form no part of the claimed design. 

CLAIM The ornamental design for a child safety seat base, as shown and described. 